1. Field of the Invention
The invention relates in general to a method of designing an active region pattern with a shift dummy pattern, and more particularly, to a method adding a shift dummy pattern into an diffusion region for the process of forming a shallow trench isolation. Therefore, a better planarization effect is obtained in the subsequent process of chemical mechanical polishing (CMP), and a circuit problem induced by various parasitic capacitors is resolved.
2. Description of the Related Art
As the design of an integrated circuit is more and more complex, the line width of fabrication process reduced narrower than 1 xcexcm causes a restriction the development of a trench isolation technique in a complementary metal-oxide-semiconductor (CMOS) is thus restricted. While performing chemical mechanical polishing for planarization, if a under layer has a pattern on which the distance between devices is over 10 xcexcm, a dishing recess is formed on the region without a device thereon after polishing. Thus, a global planarization is affected. This is called as a dishing effect. In FIG. 1A to FIG. 1D, a shallow trench isolation formed by a conventional technique of chemical mechanical polishing is shown.
In FIG. 1A, on a semiconductor substrate 10, for example, a silicon substrate, a pad oxide layer 11 and a dielectric layer 12, for example, a silicon nitride layer are formed in sequence. Using photolithography and etching, a device region 13 is formed on the substrate 10. Using a photo-resist layer (not shown) on the device region 13 as a mask, the substrate 10 is etched, for example, by anisotropic etching, to form several trenches with certain depths. In FIG. 1B, using chemical vapor deposition (CVD), an oxide layer 14 is formed over the substrate 10. The oxide layer 14 is polished by chemical mechanical polishing with the dielectric layer 12 as a stop layer, so that several trench isolations 15, 16 are formed as shown in FIG. 1C.
After the formation of trench isolations 15, 16, subsequent processes, for example, removing the pad oxide layer 11 and the dielectric layer, forming a gate oxide layer 17 and a poly-silicon layer 18, is performed as shown in FIG. 1D. As shown in the figure, the width of each trench isolation is not identical. For example, the region of trench isolation 16 is larger than the region of the trench isolation 15. The polysilicon layer 18 is well planarized on the trench isolation 15. On the contrary, the poly-silicon layer 18 on the trench isolation 15 has a smooth recess. Thus, using chemical mechanical polishing, only a local planarization is achieved. The global planarization cannot be achieved.
To resolve the drawback mentioned above, conventionally, a dummy pattern is added to the active region pattern to improve the uniformity of chemical mechanical polishing. However, a parasitic capacitance is induced by doing so to affect the performance of devices. The metal line on different dummy pattern causes a time delay by different parasitic capacitance, and therefore, causes a circuit problem. In FIG. 2, a conventional method of designing an active region pattern with a dummy pattern is shown. Metal lines 20, 22 are formed on different locations of the dummy pattern 24, and the dummy pattern 24 comprises columns 24a to 24d. For example, the metal line 20 is formed on a column 24c of the dummy pattern, and the metal line 22 covers a part of the column 24a and a part of the column 24b of the dummy pattern 24. Between the metal line 22 and the dummy pattern 24, different parasitic capacitance is induced in practical application, so that a problem of different time order, for example, an RC delay is caused.
It is therefore an object of the invention to provide a method of designing an active region pattern with a dummy pattern. By shifting a predetermined dummy pattern, the parasitic capacitance between each metal line and the dummy pattern is identical. Therefore, an identical RC time is obtained.
To achieve these objects and advantages, and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention is directed towards a method of designing an active region pattern with a dummy pattern. An integrated circuit having an original active region pattern thereon is provided. The original active region pattern is expanded with a first parameter of line width to obtain a first pattern. By subtracting the first pattern, a second pattern is obtained. A dummy pattern which comprises an array of a plurality of elements is provided. By shifting the elements, a shifted dummy pattern is obtained. The second pattern and the shifted dummy pattern are combined, so that an overlapped region thereof is extracted as a combined dummy pattern. The combined dummy pattern is expanded with a second parameter of line width, so that a resultant dummy pattern is obtained. The resultant dummy pattern is added to the first pattern, so that the active region pattern with a shifted dummy pattern is obtained.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.